§1.1. Field of the Invention
The present invention concerns wireless communications. In particular, the present invention concerns wireless distribution of video content.
§1.2. Background Information
In recent years, the demand for video applications over wireless networks has risen with the increase in both the bandwidth of wireless channels and the computational power of mobile devices. To provide efficient delivery among a group of users simultaneously, multicast has been used as an effective solution, as it saves network resources by sharing the data streams across receivers (e.g., nodes or client devices). Unfortunately, however, the use of heterogeneous receivers causes a higher packet loss ratio and higher bandwidth variations of wireless channels. This makes video multicast over wireless networks challenging.
Wireless channels can be characterized by their bursty and location dependent errors. Hence, each user in a multicast system will most likely lose different packets. Although a simple Automatic Repeat reQuest (“ARQ”) based scheme is sometimes used to request lost packets, such a scheme is not a good solution for video multicast over wireless channels since it can cause a large volume of retransmissions.
There are several studies discussing error control in video multicast over wireless networks. (See, e.g., the articles: P. Ge, P. McKinley, “Leader-Driven Multicast for Video Streaming on Wireless LANS”, Proceedings of IEEE ICN, (2002); and I. Bajic, “Efficient Error Control for Wireless Video Multicast,” Proceedings of IEEE MMSP, (2006), both incorporated herein by reference.) In a multicast scenario, the use of heterogeneous receivers is a concern since various receivers have different connection qualities and power limitations. Scalable (layered) video coding, where different numbers of layers of video data can be received by different clients with different quality reception to provide video of different quality levels, is one approach to solve the heterogeneity problem. Several researchers have studied layered video multicast in infrastructure-based wireless networks. (See, e.g., the articles: T. A. Lee, S. G. Chan, Q. Zhang, W. Zhu, and Y. Zhang, “Allocation of Layer Bandwidths and FECs for Video Multicast Over Wired an Wireless Networks,” IEEE Transactions on Circuits and Systems for Video Technology, Vol. 12, No. 12, pp. 1059-1070 (December 2002); A. Majumdar, D. Sachs, I. Kozintsev, “Multicast and Unicast Real-Time Video Streaming over Wireless LANs,” IEEE Transactions on Circuits and Systems for Video Technology, Vol. 12, pp. 524-534 (June 2002); T. Kim and M. Ammar, “A Comparison of Heterogeneous Video Multicast Schemes Layered Encoding or Stream Replication,” IEEE Transactions on Multimedia, Vol. 7, No. 6, pp. 1123-1130 (December 2005); and L. Lao, J. Cui, M. Y. Sanadidi and M. Gerla, “Scalable and Adaptive Multicast Video Streaming for Heterogeneous and Mobile Users,” Proceedings of IEEE ISWCS (2005), each of which is incorporated herein by reference.) Moreover, video multicast over ad hoc networks has been considered in the articles, S. Mao, X. Cheng, Y. T. Hou, and H. Sherali, “Multiple Tree Video Multicast Over Wireless Ad-Hoc Networks,” Proc. of IEEE BROADNETS (2004), and W. Wei and A. Zakhor, “Multiple Tree Video Multicast OverWireless Ad-Hoc Networks,” IEEE Trans. Circuits Syst. Video Technol., Vol. 17, No. 1, pg. 215 (January 2007) (both incorporated herein by reference), which propose to use multiple description video to overcome the unreliability of wireless links. However, none of these works consider the use of cooperation among receivers (e.g., nodes or client devices).
Generally, receivers may have very different channel qualities, with ones closer to the sender having better quality on average than receivers further from the sender. In a conventional multicast system, the sender adjusts its transmission rate to the receiver with the worst channel conditions (to ensure that all clients receive adequate quality video). Consequently, all receivers of the system can be severely affected if even just one receiver is affected by path loss and multipath fading, or otherwise has poor channel conditions.